1. Field of the Invention
The present invention pertains to off-axis light stimulation delivered to a person's pupils for inducing biological responses in the person without impairing vision.
2. Description of the Prior Art
One of the most fundamental characteristics of life on the earth is the way all living things change to adjust to the twenty four hour variations in the physical environment. Indeed, the majority of all biochemical, physiological and behavioral variables in humans fluctuates on a rhythmic basis with a period of about twenty four hours. It is now well established that these daily rhythms are temporally organized by a twenty four hour (i.e., circadian) clock which, in mammals, is located in the suprachlasmatic nucleus (SCN) of the hypothalamus. The circadian system maintains temporal synchronization between the organism and the external environment, as well as the optimal internal coordination of diverse physiological processes in time. The light-dark cycle is the primary environmental agent that synchronizes the endogenous clock, whose intrinsic period is almost always slightly different than twenty four hours (e.g. twenty three-twenty five hours), to the changes in the physical environment that occur within a period of twenty four hours, due to the rotation of the earth on its axis. The ability of the natural light-dark (LD) cycle to entrain circadian rhythms is based on the response of the circadian pacemaker to light. Thus, light pulses presented during early subjective night induce phase delays of the circadian clock, while light exposure during the late subjective night produces phase advances. In mammals, a special tract of nerves, referred to as the retinohypothalmic tract (RHT), carry information about the light-dark environment directly from the retina to the SCN.
Under normal conditions, there is a stable phase relationship among circadian rhythmicity, sleep, and the light-dark cycle. In animals living under natural conditions, uncoupling of sleep and circadian rhythmicity from their normal phase, relative to the entraining light-dark cycle rarely, if ever, occurs. However, humans routinely disrupt the normal synchronization of the sleep-wake and light-dark cycles, either for short periods of time (i.e., following rapid travel across time zones, referred to as the "jet lag" syndrome), or for long periods of time (i.e., as occurs in "shift-workers"). Furthermore, humans are also able to ignore signals from the circadian clock system indicating that it is time to sleep, and can also override the homeostatic need for sleep as occurs during prolonged periods of wakefulness. A number of acute and chronic adverse effects of both shift-work and jet-lag on human health, safety, performance and productivity have now been well documented.